The present invention relates to anti-static packaging material and to methods of producing such materials, and more particularly to a laminated packaging material having a semi-rigid substrate sheet of packaging material which is coated with a layer of heat-sealable, anti-static plastic material. The structure provides both mechanical support for a static-sensitive item to be packaged and a continuous electrostatic shield to protect the item from static buildup while it is being packaged. Furthermore, the heat-sealable plastic coating permits a flexible anti-static skin film to be heat sealed to the material so that it may be employed in skin-packaging systems.
Heat-sealable, anti-static packaging materials which are intended to protect static-sensitive items from damage due to triboelectric charging are known in the art. Such a material is disclosed, for example, in U.S. Pat. No. 3,572,499 to Mondano which discloses the fabrication of a laminate material consisting of a layer of metal foil which is sandwiched between an electrically conductive, heat-sealable, synthetic plastic. The material disclosed in the Mondano patent is intended to be used as a wrap or fabricated into a bag, and is not practical for use in skin-packaging operations, either as a skin-packaging film or as a relatively rigid material which can support the item being packaged. A laminated heat-sealable packaging material which is provided in sheet form and which is resistant to the penetration of grease or oil is taught in U.S. Pat. No. 3,775,239 to Snow. This packaging material, although excellent in resistance to certain specified compounds, does not provide an anti-static protection to static-sensitive components. A method of coating various surfaces with a plastic coating material to which a metallic powder has been added is taught in U.S. Pat. No. 3,085,025 to Eaton. The method of the Eaton patent includes applying a thermoplastic material to the surface to be coated followed by applying a powdered metallic matter to the thermoplastic material, and then heating the film to a viscous liquid into which the powdered matter migrates. The liquid is then cooled so that it is returned to its solid state with the powder bonded thereto. However, the object of the Eaton process is to utilize the suspended powdered metal to provide a surface appearance to the coated object, not to impart electrical characteristics such as a resistance to static discharge.
U.S. Pat. No. 3,104,985 discloses compositions of cured polyolifin which are suitable for producing conductive films by adding fillers such as carbon black to solutions of plastic. Carbon black is an unacceptable material for use in many packaging operations since it sloughs off of the plastic in which it is dissolved and contaminates the packaged items. U.S. Pat. No. 2,405,104 teaches the construction of an anti-static ordnance bag having a layer of combustible material which is inappropriate for use in skin packaging operations. A method for encapsulating rigid items in molten plastic is described in U.S. Pat. No. 3,313,089; however, no reference or teaching is made of providing anti-static material in my method step to prevent the buildup of static charges.
Other examples of various coating, packaging, or bagging techniques or materials are found in the following U.S. Pat. Nos.: 3,373,918; 3,143,364; 3,078,201; 3,057,539; 2,845,962; 2,817,604; and 2,551,087. However, such techniques and materials are not adapted for use in skin packaging operations of the type already owned and maintained by many packaging enterprises.
Therefore, a need exists for a material which is suitable for packaging static-sensitive items which combines protection of the item from exposure to electrostatic charge, mechanical support of the item while it is being packaged and handled in packaged form, and adaptability to state-of-the-art packaging techniques.
It is therefore a principle object of the present invention to provide an improved material for packaging static-sensitive items.
It is a further object of the invention to provide an anti-static packaging material which can be utilized in a heat-sealable, skin-packaging process.
Another object of the invention is to provide an anti-static, heat-sealable packaging material which provides mechanical support to the item being packaged.
Another object of the invention is to provide an anti-static heat-sealable package which is constructed from such a material.
A further object of the invention is the provision of a method for making such a material.
These and other objects of the invention will become readily apparent from the ensuing description when it is taken together with the following drawings.